The invention relates to piston and cylinder units of the type comprising a cylinder, an axially moving piston in the cylinder, a piston rod attached to the piston and extending out of the cylinder to at least one side of the piston through a supporting and sealing arrangement which coaxially completely surrounds the piston rod and is detachably connected to the cylinder. At its end nearest the interior of the cylinder this supporting and sealing arrangement has an annular sealing section, an annular stripper section axially spaced from the sealing section so as to be further away from the interior of the cylinder, and a piston rod support bushing axially between these two sections.
The purposes of such a supporting and sealing arrangement is to seal off the inside of the cylinder from the exterior, to prevent foreign matter working its way into the interior of the cylinder and to ensure accurate running, with a minimum degree of wear, of the piston rod where it extends through the cylinder wall. Such supporting and sealing arrangements as so far proposed have been made up of separate parts, one for performing each of the different functions. There is thus firstly a sealing ring having a sealing portion in the form of a sealing lip surrounding the piston rod and serving to provide the internal sealing function of the cylinder. Following this sealing ring on the outer side thereof there is then a support bushing which is in turn followed by a stripper ring with an annular stripping portion to strip dirt, dust and the like from the outer surface of the piston rod. These components are together mounted with a press fit in a cylindrical socket in the cylinder and they coaxially surround the piston rod.
A shortcoming with such a supporting and sealing arrangement as used in the prior art is firstly the slowness of assembly, which is due to the large number of individual parts. Furthermore dismounting the parts as necessary after wear has taken place is awkward, since the separate parts are tightly jammed in the cylinder and are difficult to dislodge. It is practically impossible to replace the parts without damage so that even if only the sealing ring has become worn or damaged, the two other sections of the supporting and sealing arrangement will have to be replaced as well and this increases costs. A further point is that owing to the direct longitudinal sliding of two metal parts the supporting and sealing arrangement is very prone to wear so that replacement of the support bushing is frequently called for. A further cause of wear is that the supporting bushing is rigidly mounted in the cylinder so that any inaccuracy in manufacture as regards the coaxial alignment of the support bushing and the piston rod will be compensated for by wear.